Circadian rhythms in serum melatonin from infancy to adolescence.

The circadian rhythm of circulating melatonin was determined in 38 children, aged 1-18 yr. Serum melatonin concentrations at 2400 and 0300 h in children aged 1-5 yr were significantly (P less than 0.001) higher than those in older children [6-10 yr, puberty stage 1 (P1)]. Nocturnal melatonin levels also were significantly (P less than 0.01) higher in P1 subjects than in P2 subjects aged 9-12 yr. A further small decline was found from P2 to P4/P5 (P less than 0.05). Thus, the decline in the nocturnal melatonin surge is not exclusively related to pubertal development, but begins in infancy.